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Articles 91 - 120 of 130

Full-Text Articles in Astrophysics and Astronomy

Rapid Cooling Of The Neutron Star In The Quiescent Super-Eddington Transient Xte J1701-462, Joel K. Fridriksson, Jeroen Homan, Rudy Wijnands, Mariano Méndez, Diego Altamirano, Edward M. Cackett, Edward F. Brown, Tomaso M. Belloni, Nathalie Degenaar, Walter H. G. Lewin May 2010

Rapid Cooling Of The Neutron Star In The Quiescent Super-Eddington Transient Xte J1701-462, Joel K. Fridriksson, Jeroen Homan, Rudy Wijnands, Mariano Méndez, Diego Altamirano, Edward M. Cackett, Edward F. Brown, Tomaso M. Belloni, Nathalie Degenaar, Walter H. G. Lewin

Physics and Astronomy Faculty Research Publications

We present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the 2006-2007 outburst of the super-Eddington neutron star (NS) transient XTE J1701-462, as well as Chandra and XMM-Newton observations covering the first sime800 days of the subsequent quiescent phase. The source transitioned quickly from active accretion to quiescence, with the luminosity dropping by over 3 orders of magnitude in sime13 days. The spectra obtained during quiescence exhibit both a thermal component, presumed to originate in emission from the NS surface, and a non-thermal component of uncertain origin, which has shown large and irregular variability. …

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Multiwavelength Observations Of 1rxh J173523.7-354013: Revealing An Unusual Bursting Neutron Star, N. Degenaar, P. G. Jonker, M. A. P. Torres, R. Kaur, N. Rea, G. L. Israel, A. Patruno, G. Trap, E. M. Cackett, P. D'Avanzo, G. Lo Curto, G. Novara, H. Krimm, S. T. Holland, A. De Luca, P. Esposito, R. Wijnands May 2010

Multiwavelength Observations Of 1rxh J173523.7-354013: Revealing An Unusual Bursting Neutron Star, N. Degenaar, P. G. Jonker, M. A. P. Torres, R. Kaur, N. Rea, G. L. Israel, A. Patruno, G. Trap, E. M. Cackett, P. D'Avanzo, G. Lo Curto, G. Novara, H. Krimm, S. T. Holland, A. De Luca, P. Esposito, R. Wijnands

Physics and Astronomy Faculty Research Publications

On 2008 May 14, the Burst Alert Telescope onboard the Swift mission triggered on a type-I X-ray burst from the previously unclassified ROSAT object 1RXH J173523.7-354013, establishing the source as a neutron star X-ray binary. We report on X-ray, optical and near-infrared observations of this system. The X-ray burst had a duration of ~2 h and belongs to the class of rare, intermediately long type-I X-ray bursts. From the bolometric peak flux of ~3.5 × 10-8ergcm-2s-1, we infer a source distance of D <~ 9.5 kpc. Photometry of the field reveals an optical counterpart that declined from R = 15.9 during the X-ray burst to R = 18.9 thereafter. Analysis of post-burst Swift/X-ray Telescope observations as well as archival XMM-Newton and ROSAT data suggests that the system is persistent at a 0.5-10 keV luminosity of ~2 × 1035 (D/9.5 kpc)2ergs-1. Optical and infrared photometry …

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Pulsational Mapping Of Calcium Across The Surface Of A White Dwarf, Susan E. Thompson, Ted Von Hippel, Et Al. May 2010

Pulsational Mapping Of Calcium Across The Surface Of A White Dwarf, Susan E. Thompson, Ted Von Hippel, Et Al.

Publications

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a …

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Spitzer Mid-Infrared Spectroscopy Of Compact Symmetric Objects: What Powers Radio-Loud Active Galactic Nuclei?, Kyle W. Willett, John T. Stocke, Jeremy K. Darling, Eric S. Perlman Apr 2010

Spitzer Mid-Infrared Spectroscopy Of Compact Symmetric Objects: What Powers Radio-Loud Active Galactic Nuclei?, Kyle W. Willett, John T. Stocke, Jeremy K. Darling, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

We present low- and high-resolution mid-infrared (mid-IR) spectra and photometry for eight compact symmetric objects (CSOs) taken with the Infrared Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful radio galaxies show significant diversity in their mid-IR spectra. This includes multiple atomic fine-structure lines, H2 gas, polycyclic aromatic hydrocarbon (PAH) emission, warm dust from T = 50 to150 K, and silicate features in both emission and absorption. There is no evidence in the mid-IR of a single template for CSO hosts, but 5/8 galaxies show similar moderate levels of star formation (<10 M ⊙ yr-1 from PAH emission) and silicate dust in a clumpy torus. The total amount of extinction ranges from AV ∼ 10 to 30, and the high-ionization [Ne V] 14.3 and 24.3 μm transitions are not detected for any galaxy in the sample. Almost all CSOs show contributions both from star formation and active galactic nuclei (AGNs), suggesting that they occupy a continuum between pure starbursts and AGNs. This is consistent with the hypothesis that radio galaxies are created following a galactic merger; the timing of the radio activity onset means that contributions to the IR luminosity from both merger-induced star formation and the central AGN are likely. Bondi accretion is capable of powering the radio jets for almost all CSOs in the sample; the lack of [Ne V] emission suggests an advection-dominated accretion flow mode as a possible candidate. Merging black holes (BHs) with M BH > 108 M ⊙ likely exist …

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Measuring The Spin Of Grs 1915+105 With Relativistic Disk Reflection, J. L. Blum, J. M. Miller, A. C. Fabian, M. C. Miller, J. Homan, M. Van Der Klis, E. M. Cackett, R. C. Reis Nov 2009

Measuring The Spin Of Grs 1915+105 With Relativistic Disk Reflection, J. L. Blum, J. M. Miller, A. C. Fabian, M. C. Miller, J. Homan, M. Van Der Klis, E. M. Cackett, R. C. Reis

Physics and Astronomy Faculty Research Publications

GRS 1915+105 harbors one of the most massive known stellar black holes in the Galaxy. In 2007 May, we observed GRS 1915+105 for ~117 ks in the low/hard state using Suzaku. We collected and analyzed the data with the Hard X-ray Detector/Positive Intrinsic Negative and X-ray Spectrometer cameras spanning the energy range from 2.3 to 55 keV. Fits to the spectra with simple models reveal strong disk reflection through an Fe K emission line and a Compton backscattering hump. We report constraints on the spin parameter of the black hole in GRS 1915 + 105 using relativistic disk reflection models. …

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Constraining The Spin Of The Black Hole In Fairall 9 With Suzaku, S. Schmoll, J. M. Miller, M. Volonteri, E. Cackett, C. S. Reynolds, A. C. Fabian, L. W. Brenneman, G. Miniutti, L. C. Gallo Oct 2009

Constraining The Spin Of The Black Hole In Fairall 9 With Suzaku, S. Schmoll, J. M. Miller, M. Volonteri, E. Cackett, C. S. Reynolds, A. C. Fabian, L. W. Brenneman, G. Miniutti, L. C. Gallo

Physics and Astronomy Faculty Research Publications

We report on the results of spectral fits made to data obtained from a 168 ks Suzaku observation of the Seyfert 1 galaxy Fairall 9. The source is clearly detected out to 30 keV. The observed spectrum is fairly simple; it is well described by a power law with soft excess and disk reflection. A broad iron line is detected, and easily separated from distinct narrow components owing to the resolution of the CCDs in the X-ray Imaging Spectrometer (XIS). The broad line is revealed to be asymmetric, consistent with a disk origin. We fit the XIS and Hard X-ray …

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Chandra And Swift Observations Of The Quasi-Persistent Neutron Star Transient Exo 0748-676 Back To Quiescence, N. Degenaar, R. Wijnands, M. T. Wolff, P. S. Ray, K. S. Wood, J. Homan, W. H. G. Lewin, P. G. Jonker, E. M. Cackett, J. M. Miller, E. F. Brown Jun 2009

Chandra And Swift Observations Of The Quasi-Persistent Neutron Star Transient Exo 0748-676 Back To Quiescence, N. Degenaar, R. Wijnands, M. T. Wolff, P. S. Ray, K. S. Wood, J. Homan, W. H. G. Lewin, P. G. Jonker, E. M. Cackett, J. M. Miller, E. F. Brown

Physics and Astronomy Faculty Research Publications

The quasi-persistent neutron star X-ray transient and eclipsing binary EXO 0748-676 recently started the transition to quiescence following an accretion outburst that lasted more than 24 years. We report on two Chandra and 12 Swift observations performed within five months after the end of the outburst. The Chandra spectrum is composed of a soft, thermal component that fits to a neutron star atmosphere model with kT∞ ~ 0.12keV, joined by a hard power-law tail that contributes ~20 per cent of the total 0.5-10 keV unabsorbed flux. The combined Chandra/Swift data set reveals a relatively hot and luminous quiescent system …

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Suzaku Observations Of The Black Hole H1743-322 In Outburst, J. L. Blum, J. M. Miller, E. Cackett, K. Yamaoka, H. Takahashi, J. Raymond, C. S. Reynolds, A. C. Fabian Apr 2009

Suzaku Observations Of The Black Hole H1743-322 In Outburst, J. L. Blum, J. M. Miller, E. Cackett, K. Yamaoka, H. Takahashi, J. Raymond, C. S. Reynolds, A. C. Fabian

Physics and Astronomy Faculty Research Publications

We observed the Galactic black hole candidate H1743-322 with Suzaku for approximately 32 ks, while the source was in a low/hard state during its 2008 outburst. We collected and analyzed the data with the HXD/PIN, HXD/GSO, and XIS cameras spanning the energy range 0.7-200 keV. Fits to the spectra with simple models fail to detect narrow Fe XXV and Fe XXVI absorption lines, with 90% confidence upper limits of 3.5 and 2.5 eV on the equivalent width, respectively. These limits are commensurate with those in the very high state, but are well below the equivalent widths of lines detected in …

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A Deep Xmm-Newton Observation Of The Quasar 3c 287, G. Salvesen, J. M. Miller, E. Cackett, A. Siemiginowska Feb 2009

A Deep Xmm-Newton Observation Of The Quasar 3c 287, G. Salvesen, J. M. Miller, E. Cackett, A. Siemiginowska

Physics and Astronomy Faculty Research Publications

We report on an XMM-Newton observation of the z = 1.055 quasar and Gigahertz Peaked Spectrum (GPS) source 3C 287. Our 62.3 ks observation provides an exceptional X-ray view of a prominent member of this important subclass of active galactic nuclei (AGNs). The X-ray spectra of 3C 287 are consistent with a simple absorbed power law with a spectral index of Γ = 1.72 ± 0.02. Our fits imply a bolometric luminosity of L = 5.8 ± 0.2 × 1045 erg s-1 over the 0.3-10.0 keV band; this gives a mass lower limit of M BH min >= …

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Grb060602b = Swift J1749.4-2807: An Unusual Transiently Accreting Neutron-Star X-Ray Binary, R. Wijnands, E. Rol, E. Cackett, R. L. C. Starling, R. A. Remillard Feb 2009

Grb060602b = Swift J1749.4-2807: An Unusual Transiently Accreting Neutron-Star X-Ray Binary, R. Wijnands, E. Rol, E. Cackett, R. L. C. Starling, R. A. Remillard

Physics and Astronomy Faculty Research Publications

We present an analysis of the Swift Burst Alert Telescope (BAT) and X-ray telescope (XRT) data of GRB060602B, which is most likely an accreting neutron star in a binary system and not a gamma-ray burst. Our analysis shows that the BAT burst spectrum is consistent with a thermonuclear flash (type I X-ray burst) from the surface of an accreting neutron star in a binary system. The X-ray binary nature is further confirmed by the report of a detection of a faint point source at the position of the XRT counterpart of the burst in archival XMM-Newton data approximately six year …

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A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands Jan 2009

A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands

Physics and Astronomy Faculty Research Publications

While iron emission lines are well studied in black hole systems, both in X-ray binaries and active galactic nuclei, there has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent observations with Suzaku and XMM-Newton have revealed broad, asymmetric iron line profiles in three neutron star LMXBs, confirming an inner disk origin for these lines in neutron star systems. Here, we present a search for iron lines in six neutron star LMXBs. For each object we have simultaneous Chandra and RXTE observations at two separate epochs, allowing for both a high-resolution spectrum …

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Winds And Accretion In Young Stars, Suzan Edwards Jan 2009

Winds And Accretion In Young Stars, Suzan Edwards

Astronomy: Faculty Publications

Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star‐disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin‐up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new …

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Redshifted Absorption At He I Λ10830 As A Probe Of The Accretion Geometry Of T Tauri Stars, William Fischer, John Kwan, Suzan Edwards, Lynne A. Hillenbrand Nov 2008

Redshifted Absorption At He I Λ10830 As A Probe Of The Accretion Geometry Of T Tauri Stars, William Fischer, John Kwan, Suzan Edwards, Lynne A. Hillenbrand

Astronomy: Faculty Publications

We probe the geometry of magnetospheric accretion in classical T Tauri stars (CTTSs) by modeling red absorption at He I λ10830 via scattering of the stellar and veiling continua. Under the assumptions that the accretion flow is an azimuthally symmetric dipole and helium is sufficiently optically thick that all incident 1 μm radiation is scattered, we illustrate the sensitivity of He I λ10830 red absorption to both the size of the magnetosphere and the filling factor of the hot accretion shock. We compare model profiles to those observed in 21 CTTSs with subcontinuum redshifted absorption at He I λ10830 and …

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Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel Aug 2008

Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel

Publications

Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide. We also investigate the effect that time-variable accretion has on the metal abundances of different species, and we show how this can …

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Sph Simulations Of Direct Impact Accretion In The Ultracompact Am Cvn Binaries, Joshua Dolence, Matt A. Wood, Isaac Silver Aug 2008

Sph Simulations Of Direct Impact Accretion In The Ultracompact Am Cvn Binaries, Joshua Dolence, Matt A. Wood, Isaac Silver

Aerospace, Physics, and Space Science Faculty Publications

The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527), a two-member subclass of the AM CVn stars, continue to generate interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three are significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs, in which the accretion stream impacts the surface of a rapidly rotating primary white dwarf directly, but at a …

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Investigating The Nature Of Absorption Lines In The Chandra X-Ray Spectra Of The Neutron Star Binary 4u 1820-30, E. M. Cackett, J. M. Miller, J. Raymond, J. Homan, M. Van Der Klis, M. Méndez, D. Steeghs, R. Wijnands Apr 2008

Investigating The Nature Of Absorption Lines In The Chandra X-Ray Spectra Of The Neutron Star Binary 4u 1820-30, E. M. Cackett, J. M. Miller, J. Raymond, J. Homan, M. Van Der Klis, M. Méndez, D. Steeghs, R. Wijnands

Physics and Astronomy Faculty Research Publications

We use four Chandra gratings spectra of the neutron star low-mass X-ray binary 4U 1820-30 to better understand the nature of certain X-ray absorption lines in X-ray binaries, including the Ne II, Ne III, Ne IX, O VII, and O VIII lines. The equivalent widths of the lines are generally consistent between the observations, as expected if these lines originate in the hot interstellar medium. No evidence was found that the lines were blueshifted, again supporting the interstellar medium origin, although this may be due to poor statistics. There is apparent variability in the O VIII Lyα line equivalent width …

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Relativistic Iron Emission Lines In Neutron Star Low-Mass X-Ray Binaries As Probes Of Neutron Star Radii, Edward M. Cackett, Jon M. Miller, Sudip Bhattacharyya, Jonathan E. Grindlay, Jeroen Homan, Michiel Van Der Klis, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands Feb 2008

Relativistic Iron Emission Lines In Neutron Star Low-Mass X-Ray Binaries As Probes Of Neutron Star Radii, Edward M. Cackett, Jon M. Miller, Sudip Bhattacharyya, Jonathan E. Grindlay, Jeroen Homan, Michiel Van Der Klis, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands

Physics and Astronomy Faculty Research Publications

Using Suzaku observations of three neutron star low-mass X-ray binaries (Ser X-1, 4U 1820-30, and GX 349+2) we have found broad, asymmetric, relativistic Fe K emission lines in all three objects. These Fe K lines can be well fit by a model for lines from a relativistic accretion disk (``diskline''), allowing a measurement of the inner radius of the accretion disk and hence an upper limit on the neutron star radius. These upper limits correspond to 14.5-16.5 km for a 1.4 Msolar neutron star. The inner disk radii that we measure with Fe K lines are in good agreement …

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The New Class Of Dusty Daz White Dwarfs, Ted Von Hippel, Et Al. Jun 2007

The New Class Of Dusty Daz White Dwarfs, Ted Von Hippel, Et Al.

Publications

Our mid-infrared survey of 124 white dwarfs with the Spitzer Space Telescope and the IRAC imager has revealed an infrared excess associated with the white dwarf WD 2115-560 naturally explained by circumstellar dust. This object is the fourth white dwarf observed to have circumstellar dust. All four are DAZ white dwarfs, i.e., they have both photospheric Balmer lines and photospheric metal lines. We discuss these four objects as a class, which we abbreviate "DAZd," where the "d" stands for "dust." Using an optically thick, geometrically thin disk model analogous to Saturn's rings, we find that the inner disk edges are …

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The Physical Origin Of Negative Superhumps In Cataclysmic Variables, Matt A. Wood, Christopher J. Burke Jun 2007

The Physical Origin Of Negative Superhumps In Cataclysmic Variables, Matt A. Wood, Christopher J. Burke

Aerospace, Physics, and Space Science Faculty Publications

It has been suspected for over 20 years that the observed negative superhumps in cataclysmic variables are due to the retrograde precession of a tilted disk. We present new smooth particle hydrodynamics simulation results that demonstrate that the source of the modulation of the luminosity of the light in a negatively superhumping cataclysmic variable is the transit of the bright spot across the face of an accretion disk that is tilted out of the orbital plane. In an untilted disk the bright spot is always located on the outer edge of the disk, and the intrinsic brightness of the accretion …

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Discovery Of Photospheric Calcium Line-Strength Variations In The Dazd White Dwarf G29-38, Ted Von Hippel, Susan E. Thompson May 2007

Discovery Of Photospheric Calcium Line-Strength Variations In The Dazd White Dwarf G29-38, Ted Von Hippel, Susan E. Thompson

Publications

Metals in the photospheres of white dwarfs with Teff between 12,000 and 25,000 K should gravitationally settle out of these atmospheres in 1 ̶ 2 weeks. Temporal variations in the line strengths of these metals could provide a direct measurement of episodic metal accretion. Using archival VLT and Keck spectroscopy, we find evidence that the DAZd white dwarf G29-38 shows significant changes in its Ca П K line strength. At the two best-observed epochs, we find that the Ca line equivalent width (EW) = 165 ̶ 4 mǺ (in 1996.885) and 280 ± 8 mǺ (in 1999.653), which is …

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Warm Gas In The Inner Disks Around Young Intermediate-Mass Stars, Sean D. Brittain, Theodore Simon, Joan R. Najita, Terrence W. Rettig Apr 2007

Warm Gas In The Inner Disks Around Young Intermediate-Mass Stars, Sean D. Brittain, Theodore Simon, Joan R. Najita, Terrence W. Rettig

Publications

The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K- and M-band spectroscopy of 14 intermediate-mass young stars. In sources that have optically thick inner disks, i.e., E(K-L)>1, our detection rate of the rovibrational CO transitions is 100%, and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the rovibrational CO transitions from HD 141569. In this case, we show that the …

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Further Evidence For Variable Synchrotron Emission In Xte J1118+480 In Outburst, Robert I. Hynes, Edward L. Robinson, Kevin J. Pearson, Dawn M. Gelino, Wei Cui, Yongquan Xue, Matt A. Wood, Todd K. Watson, Don Earl Winget, Isaac M. Silver Nov 2006

Further Evidence For Variable Synchrotron Emission In Xte J1118+480 In Outburst, Robert I. Hynes, Edward L. Robinson, Kevin J. Pearson, Dawn M. Gelino, Wei Cui, Yongquan Xue, Matt A. Wood, Todd K. Watson, Don Earl Winget, Isaac M. Silver

Aerospace, Physics, and Space Science Faculty Publications

We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE Jill 8+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ∼10 s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHKS photometry, as in the previous outburst, exhibits especially large-amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power law of slope α = -0.78 ± 0.07, where Fᵧ …

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Cooling Of The Quasi-Persistent Neutron Star X-Ray Transients Ks 1731-260 And Mxb 1659-29, Edward M. Cackett, Rudy Wijnands, Manuel Linares, Jon M. Miller, Jeroen Homan, Walter H. G. Lewin Oct 2006

Cooling Of The Quasi-Persistent Neutron Star X-Ray Transients Ks 1731-260 And Mxb 1659-29, Edward M. Cackett, Rudy Wijnands, Manuel Linares, Jon M. Miller, Jeroen Homan, Walter H. G. Lewin

Physics and Astronomy Faculty Research Publications

We present Chandra and XMM-Newton X-ray observations that monitor the neutron star cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29 for approximately 4 yr after these sources returned to quiescence from prolonged outbursts. In both sources the outbursts were long enough to significantly heat the neutron star crust out of thermal equilibrium with the core. We analyse the X-ray spectra by fitting absorbed neutron star atmosphere models to the observations. The results of our analysis strengthen the preliminary findings of Wijnands et al. that in both sources the neutron star crust cools down very rapidly …

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The Noao Fundamental Plane Survey - Iii. Variations In The Stellar Populations Of Red-Sequence Galaxies From The Cluster Core To The Virial Radius, Russell J. S. Smith, Michael J. Hudson, John R. Lucey, Jenica E. Nelan, Gary A. Wegner Feb 2006

The Noao Fundamental Plane Survey - Iii. Variations In The Stellar Populations Of Red-Sequence Galaxies From The Cluster Core To The Virial Radius, Russell J. S. Smith, Michael J. Hudson, John R. Lucey, Jenica E. Nelan, Gary A. Wegner

Dartmouth Scholarship

We analyse absorption line-strength indices for ~3000 red-sequence galaxies in 94 nearby clusters, to investigate systematic variations of their stellar content with location in the host cluster. The data are drawn from the NOAO Fundamental Plane Survey. Our adopted method is a generalization of that introduced by Nelan et al. to determine the global age-mass and metallicity-mass relations from the same survey. We find strong evidence for a change in galaxy properties, at fixed mass, over a range from the cluster centre to the virial radius, R_200. For example, red-sequence galaxies further out in the clusters have weaker Mgb5177 (at …

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Near-Infrared And The Inner Regions Of Protoplanetary Disks, Dejan Vinković, Željko Ivezić, Tomislav Jurkić, Moshe Elitzur Jan 2006

Near-Infrared And The Inner Regions Of Protoplanetary Disks, Dejan Vinković, Željko Ivezić, Tomislav Jurkić, Moshe Elitzur

Physics and Astronomy Faculty Publications

We examine the “puffed-up inner disk” model proposed by Dullemond, Dominik, & Natta for explaining the near-IR excess radiation from Herbig Ae/Be stars. Detailed model computations show that the observed near-IR excess requires more hot dust than is contained in the puffed-up disk rim. The rim can produce the observed near-IR excess only if its dust has perfectly gray opacity, but such dust is in conflict with the observed 10 μm spectral feature. We find that a compact (~10 AU), tenuous (τV ≲ 0.4), dusty halo around the disk inner regions contains enough dust to readily explain …

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Dq Herculis In Profile: Whole Earth Telescope Observations And Smoothed Particle Hydrodynamics Simulations Of An Edge-On Cataclysmic Variable System, Matt A. Wood Nov 2005

Dq Herculis In Profile: Whole Earth Telescope Observations And Smoothed Particle Hydrodynamics Simulations Of An Edge-On Cataclysmic Variable System, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

The old nova DQ Herculis was the Whole Earth Telescope Northern Hemisphere target for the 1997 July campaign and was observed on four nights with the SARA 0.9 m telescope during 2003 June. We present updated ephemerides for the eclipse and 71 s timings. The Fourier transform displays power at the presumed white dwarf spin period of 71.0655 s, but no significant power at either 142 or 35.5 s. The mean pulsed light curve is obtained by folding on the orbital period modulus the mean ephemeris of the 71 s period, and from this we calculate an O - C …

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Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King Aug 2005

Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King

Publications

The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the …

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The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King Aug 2004

The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King

Publications

In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow ”Li-peak” at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most …

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Dust Emission From Herbig Ae/Be Stars: Evidence For Disks And Envelopes, Anatoly Miroshnichenko, Željko Ivezić, Dejan Vinković, Moshe Elitzur Aug 1999

Dust Emission From Herbig Ae/Be Stars: Evidence For Disks And Envelopes, Anatoly Miroshnichenko, Željko Ivezić, Dejan Vinković, Moshe Elitzur

Physics and Astronomy Faculty Publications

Infrared and millimeter-wave emission from Herbig Ae/Be stars has produced conflicting conclusions regarding the dust geometry in these objects. We show that the compact dimensions of the millimeter-wave-emitting regions are a decisive indication for disks. But a disk cannot explain the spectral energy distribution unless it is embedded in an extended envelope that (1) dominates the IR emission and (2) provides additional disk heating on top of the direct stellar radiation. Detailed radiative transfer calculations based on the simplest model for envelope-embedded disks successfully fit the data from UV to millimeter wavelengths and show that the disks have central holes. …

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The Pg X-Ray Qso Sample: Links Between The Ultraviolet-X-Ray Continuum And Emission Lines, Beverley J. Wills, A. Laor, M. S. Brotherton, D. Wills, B. J. Wilkes, Gary J. Ferland, Zhaohui Shang Apr 1999

The Pg X-Ray Qso Sample: Links Between The Ultraviolet-X-Ray Continuum And Emission Lines, Beverley J. Wills, A. Laor, M. S. Brotherton, D. Wills, B. J. Wilkes, Gary J. Ferland, Zhaohui Shang

Physics and Astronomy Faculty Publications

Two sets of relationships relate QSO UV to soft X-ray continua with the broad-line region. These are (i) the Baldwin relationships, which are inverse relationships between the broad-line equivalent width and the continuum luminosity, and (ii) Boroson & Green's optical "Principal Component 1'' relationships, linking steeper soft X-ray spectra with narrower Hβ emission, stronger Hβ blue wings, stronger optical Fe II emission, and weaker [O III] λ5007 lines. In order to understand these relationships, we extended the spectra into the UV for 22 QSOs with high-quality soft X-ray spectra. These are from the complete sample of QSOs from the Bright …

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